There was a significant enrichment of IL-17+ T cells in the joints of children with extended oligoarticular JIA, the more severe form of JIA (median 2.1; IQR 1.3–4.8), as compared with persistent oligoarticular JIA, the milder form of the disease, which is self-remitting (median 0.91; IQR 0.6–2.8 [P = 0.046]) (Figure 1C). Here, IL17A is linked to juvenile idiopathic arthritis.